Playa Palenque is nice and during the week a bit more quiet. We went on the weekend and it was pretty packed.
Playa Palenque is lovely and safe. You'll find lots of middle to upper class Dominicans there, and a bunch of Europeans who winter there. A rare American might wander in. It's quiet with good food and cold beers available. (We like Elidania's and Dona Mary's best - and Cheo's Empanadas are yummmmy - he's Dona Mary's son). Not a lot of annoying vendors.
Now if you're looking for scads of Dominicans, merengue and bachata blaring, few or no foreigners, then go to Playa Najayo. Coming from the capital it's the beach before Palenque. On the weekends Dominicans arrive by the busload to party, and they need people directing cars to park.